Blood gas analysis is a commonly performed blood test used to evaluate the dissolved gas balance and acidity of a blood sample, as well as selected electrolyte levels. A blood sample is drawn from the patient into a sample container, such as syringe, and placed into a blood gas analyzer to be evaluated. Typically, the blood analyzer inserts electrodes surrounded by a semi-permeable membrane into the sample to create a potential across in the membrane drawing hydrogen ions through the membrane. The hydrogen ion activity is measured to determine the acidity of the sample. This method of the blood gas analysis, along with the analyses of other gases and/or electrolytes, requires that the blood remain in the liquid phase throughout the analysis. In addition, if the blood coagulates within the analyzer, the analyzer must be cleaned or may become damaged. As a result, an anti-coagulant, such as heparin, is normally introduced into the blood sample prior to the sample being inserted into the analyzer to prevent the blood from coagulating during testing and thereby eliminating the drawbacks associated with coagulated blood samples.
A common approach to introducing electrolyte balanced heparin into a blood sample is to first draw a liquid heparin aliquot into the syringe that is to be used to draw blood. The majority of the heparin aliquot is then expelled leaving either a small amount of liquid heparin in the syringe or a heparin coating on the internal walls of the syringe. A drawback of this approach is that actuating the syringe to draw or expel heparin can introduce air bubbles into the syringe. In addition to the health risks of introducing air bubbles into the blood stream while drawing the blood sample, any air bubbles in the blood sample can significantly alter the resulting blood gas analysis.
Another common approach is preloading a container with heparin by atomizing the liquid heparin onto the interior of the container and then subsequently drying as described in US Patent Publication No. 2003/0120198. A drawback of atomizing the heparin into a container and then subsequently drying it is that the resulting heparin composition has a glassy consistency, which makes it difficult for quick dissolution of the heparin in a blood sample. A similar drawback is that the dosage of heparin applied, which may have a varying heparin activity from production lot to lot, is limited by the surface area of the container.
Another approach to introducing heparin is to place a tablet or pledget of heparin within the container that dissolves when the blood sample is drawn into the container. This approach is described in U.S. Pat. Nos. 5,093,263 and 5,916,202. Although the dosage of heparin can be varied with this approach, the container must be agitated to dissolve and distribute the heparin throughout the sample. Another drawback is that the rate of dissolution of the heparin is limited by the surface area of the tablet or pledget. If the heparin is not effectively or quickly mixed, portions of the sample may coagulate preventing effective analysis of the blood sample. A common source of this problem is medical personnel who draw the blood sample without sufficiently agitating the container to dissolve and mix the heparin throughout the blood sample.
Thus, although heparin is commonly used as an anti-coagulant for blood gas samples, there remains a need for an anti-coagulant for blood samples with an efficient rate of dissolution. In particular, the current approaches are dependent on medical personnel sufficiently agitating the blood sample to properly dissolve the heparin throughout the blood sample. It is also always desirable to find alternative solutions to blood sample management.